feat(website): brand layer — teal palette, table logo, wordmark, footer

Anchor the site to the product's identity (Phase B branding):
- Accent palette mapped to the app's in-TUI teal (--sl-color-accent-*,
  light + dark); trim the splash hero's oversized desktop bottom padding.
- Header logo: a database-table glyph with a teal primary-key cell
  (light/dark variants); favicon redrawn to match.
- Landing wordmark 'RELational PLAYground': teal picks out REL+PLAY
  ('relplay', the domain) and R/D/B/M/S (spelling out RDBMS). Sizes
  locked in em off one master scale so the lockup zooms as a rigid unit.
- Footer override: default footer + an understated company (Lazy
  Evaluation Ltd) and source/issues line.

No engine names or 'DSL' in user-facing copy.

website/src/assets/relplay-logo-dark.svg

@@ -0,0 +1,7 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg" role="img" aria-label="RDBMS Playground">
+  <rect x="3.5" y="5" width="17" height="14" rx="2.4" stroke="#E6E6E6" stroke-width="1.7"/>
+  <path d="M3.5 9.6h17" stroke="#E6E6E6" stroke-width="1.5"/>
+  <path d="M11 5v14" stroke="#E6E6E6" stroke-width="1.3" opacity="0.55"/>
+  <path d="M3.5 14.3h17" stroke="#E6E6E6" stroke-width="1.3" opacity="0.4"/>
+  <circle cx="7.1" cy="7.3" r="1.45" fill="#56B6C2"/>
+</svg>

website/src/assets/relplay-logo-light.svg

@@ -0,0 +1,7 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg" role="img" aria-label="RDBMS Playground">
+  <rect x="3.5" y="5" width="17" height="14" rx="2.4" stroke="#1A1F2C" stroke-width="1.7"/>
+  <path d="M3.5 9.6h17" stroke="#1A1F2C" stroke-width="1.5"/>
+  <path d="M11 5v14" stroke="#1A1F2C" stroke-width="1.3" opacity="0.6"/>
+  <path d="M3.5 14.3h17" stroke="#1A1F2C" stroke-width="1.3" opacity="0.45"/>
+  <circle cx="7.1" cy="7.3" r="1.45" fill="#0F6B76"/>
+</svg>